Drug-eluting stent and delivery system with tapered stent in shoulder region

ABSTRACT

A drug-eluting stent delivery system for the treatment of edge restenosis in a blood vessel. The drug-eluting stent delivery system has a balloon disposed about at least a portion of a catheter, the balloon having a first end and a second end and a working length therebetween, the first end and the second end each including a tapered portion, each tapered portion being attached to the catheter, the balloon being inflatable from a collapsed configuration to an inflated configuration. A drug-eluting stent contacts a wall of the blood vessel to maintain the patency of the vessel. The drug-eluting stent has a first end and a second end, the first end and the second end each including a tapered portion, wherein the drug-eluting stent is disposed over the balloon such that at least a portion of the first end and the second end of the balloon are covered by the tapered drug-eluting stent. A method for making the same is also disclosed herein.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of U.S. Ser. No. 10/353,219 filed Jan.27, 2003 which issued as U.S. Pat. No. 7,156,869 on Jan. 2, 2007, theentirety of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to vascular repair devices, and in particularintravascular stents, which are adapted to be implanted into a patient'sbody lumen, such as a blood vessel or coronary artery, to maintain thepatency thereof. Stents are particularly useful in the treatment ofatherosclerotic stenosis in arteries and blood vessels. Moreparticularly, the invention concerns a tapered drug-eluting stentdelivery system consisting of an intravascular device having a localdrug-eluting component that is capable of eluting therapeutic drugs withuniform and controlled drug distribution at a treatment site whilecovering at least a portion of, or all of, a balloon shoulder or taperregion such that when deployed the stent extends to the point in thearterial wall where the artery is at reference vessel size.

Intravascular interventional devices such as stents are typicallyimplanted within a vessel in a contracted state, and expanded when inplace in the vessel in order to maintain the patency of the vessel toallow fluid flow through the vessel. Stents have a support structuresuch as a metallic structure to provide the strength required tomaintain the patency of the vessel in which it is to be implanted, andare often provided with an exterior surface coating to provide abiocompatible and/or hemocompatible surface. Since it is often useful toprovide localized therapeutic pharmacological treatment of a bloodvessel at the location being treated with the stent, it is alsodesirable to provide intravascular interventional devices such as stentswith a biocompatible and/or hemocompatible surface coating of apolymeric material with the capability of being loaded with therapeuticagents, to function together with the intravascular devices forplacement and release of the therapeutic drugs at a specificintravascular site.

Drug-eluting stent devices have shown great promise in treating coronaryartery disease, specifically in terms of reopening and restoring bloodflow in arteries stenosed by atherosclerosis. Restenosis rates afterusing drug-eluting stents during percutaneous intervention aresignificantly lower compared to bare metal stenting and balloonangioplasty. However, it appears that another phenomena which limits theperformance of drug-eluting stent devices has emerged. Recent studieshave indicated that the commonly called “candy-wrapper” effect isgenuine in drug-eluting stent devices and is a definite limiting factorin their performance. The term “candy-wrapper” effect refers to theoccurrence of in-segment or edge restenosis in a vessel treated byintravascular intervention. “Candy-wrapper” ends may result from anon-uniform drug dose at the ends of the stent and/or excessive vesselinjury at the stent margins and in the shoulder region. The“candy-wrapper” effect typically starts at the proximal and distal edgesof a treatment region and extends outward about 3 mm to 5 mm or more.Several potential reasons for this effect, many of which were firstarticulated in response to the candy wrapper effects seen withradioactive stents, include the following: (1) balloon injury outside ofthe stented area; (2) a stimulatory effect on the tissues by the activeagent at the lower concentrations outside of the stent; (3) geographicmiss during stent placement which implies the stenosis was somewhatthere to begin with; and (4) an especially large amount of vessel injuryat the stent edge itself as that is a point of maximum wall stress. Ofthe aforementioned reasons, the first and fourth reasons are the mostplausible. Accordingly, if such reasons are true, edge restenosis occursbecause the drug tissue concentration falls off rapidly outside of thestent.

What has been needed and heretofore unavailable in the art is adrug-eluting stent delivery system that would be effective in thetreatment of edge restenosis within the reference vessel. By minimizingvessel injury outside the stented section of the vessel, the occurrenceof edge effects will likely be reduced. Thus, it would be desirable tohave a drug-eluting stent that is optimally designed to have tapered endportions so that the region of drug treatment would be extended into thestent shoulder regions of the vessel. The present invention meets theseand other needs.

SUMMARY OF THE INVENTION

The present invention is directed to intraluminal devices, and moreparticularly, to a drug-eluting stent delivery system for the treatmentof edge restenosis in the region outside the stented section of areference vessel. The present invention includes a drug-eluting stenthaving tapered end portions that extend the region of drug treatmentinto the stent shoulder regions of the vessel. A method for making sucha drug-eluting stent delivery system for implantation within a vessel isalso disclosed herein.

The drug-eluting stent embodying features of the invention can bereadily delivered to the desired body lumen, such as a coronary orcarotid artery (peripheral vessels, bile ducts, etc.), by mounting thedrug-eluting stent on an expandable member of a delivery catheter, forexample a balloon, and advancing the catheter and drug-eluting stentassembly through the body lumen to the target site. Generally, thedrug-eluting stent is compressed or crimped onto the balloon portion ofthe catheter so that the drug-eluting stent does not move longitudinallyrelative to the balloon portion of the catheter during delivery throughthe arteries, and during expansion of the drug-eluting stent at thetarget site. The drug-eluting stent is relatively flexible along itslongitudinal axis to facilitate delivery through tortuous body lumensyet is stiff and stable enough radially in an expanded condition tomaintain the patency of a body lumen such as an artery when implantedtherein.

The design of the present invention tapered, drug-eluting stent deliverysystem is not without its challenges. For example, as the stent coversthe balloon tapers, during inflation one cannot count on the balloon“dog boning” to maintain the stent on the balloon. In particular, aphenomenon referred to as “watermelon seeding” can occur during stentexpansion where the stent “squirts” off to one side. This can beprevented by the dog bone shape of the balloon, which captures thestent. It can be appreciated that processes to improve stent retentionare often applied where the balloon outside of the stent issimultaneously heated and pressurized while a physical constraintsurrounds the stent to keep the stent from expanding. This processexpands the balloon out slightly at just the stent margins to helpcapture the stent and improve retention. Such processes are not aseffective in this case as there are no balloon tapers outside of thestent. One solution to stent retention where the stent covers all, or aportion of, the balloon tapers is to use a process where the entireballoon length is heated and pressurized with a constraint around thesystem. The stent is imprinted or otherwise partially embedded into theballoon along its entire length so that portions of the balloon extendin between the stent struts, thereby assisting in gripping or holdingthe stent on the balloon.

In one aspect of the present invention, the drug-eluting stent deliverysystem of the invention generally provides for a catheter tube. Aballoon is disposed about at least a portion of the catheter with theballoon having a first end and a second end and a working lengththerebetween. Each balloon end includes a tapered portion with eachtapered portion being attached to the catheter. The balloon isinflatable from a collapsed configuration, wherein the working lengthand at least a portion of each tapered portion are substantiallyflattened to an inflated configuration. The invention further includes adrug-eluting stent that contacts the walls of a lumen to maintain thepatency of the vessel with the drug-eluting stent having tapered firstand second ends. The drug-eluting stent is disposed over the balloonsuch that at least a portion of the tapered balloon first and secondends are covered by the drug-eluting stent. A therapeutic drug is loadedinto the drug-eluting stent for the eventual release thereof at atreatment site.

As will be appreciated by those having ordinary skill in the art, thedrug-eluting stent used in accordance with the present invention can bevirtually of any type. Any particular drug-eluting stent describedherein is for example purposes and not meant to be limiting of theinvention.

The drug-eluting stent further includes a pattern of struts having aplurality of flexible cylindrical rings being expandable in a radialdirection with each of the rings having a first delivery diameter and asecond implanted diameter while aligned on a common longitudinal axis.At least one link of the drug-eluting stent is attached between adjacentrings to form the drug-eluting stent structure. The pattern of strutscan be configured such that the number of cylindrical rings in eachtapered portion of the drug-eluting stent first and second ends is lessthan that in the remainder of the drug-eluting stent. In addition, thenumber of rings per unit length (i.e., length density) can be less inthe tapered regions. The drug-eluting stent includes a central portionthat can be expanded to a size greater than that of the reference vesseland the balloon tapered portions.

In one aspect of the present invention, the drug-eluting stent may beformed at least in part of a metallic material. Examples of suchmetallic materials include stainless steel, platinum, titanium,tantalum, nickel-titanium, cobalt-chromium, and alloys thereof.

The therapeutic drug loaded into the drug-eluting stent of the presentinvention can include antiplatelets, anticoagulants, antifibrins,antiinflammatories, antithrombins, and antiproliferatives. Theseforegoing types of therapeutic drugs, used to treat or preventrestenosis, are provided by way of example and are not meant to belimiting, since other types of therapeutic drugs may be developed whichare equally applicable for use with the present invention. Furthermore,the calculation of dosages, dosage rates and appropriate duration oftreatment are previously known in the art.

In one aspect of the present invention, each tapered portion of theballoon first and second ends has a length in a range of from about 1 mmup to about 10 mm for the taper. A balloon seal (not shown) having alength of from about 0.25 mm up to about 0.5 mm is not included in eachballoon tapered portion. The tapered portion of the balloon in thecollapsed configuration defines an edge, the edge defining an acuteangle measuring between 2 and 30 degrees relative to the longitudinalaxis of the catheter. The tapered first and second ends of the balloonare completely covered by the drug-eluting stent. Each tapered portionof the drug-eluting stent first and second ends has a length in a rangeof from about 1 mm up to about 8 mm, a strut thickness in a range offrom about 40 microns up to about 170 microns, and a total outerdiameter in a range of from about 0.9 mm up to about 2 mm. The taperedportion of the drug-eluting stent defines an edge, the edge defining anacute angle measuring between 2 and 30 degrees relative to thelongitudinal axis of the catheter.

In another aspect, the invention provides a drug-eluting stent deliverysystem for the treatment of edge restenosis in a blood vessel. Theinvention includes a tubular catheter. A balloon is disposed about atleast a portion of the catheter with the balloon having first and secondends and a working length therebetween. Each balloon end has a taperedportion with each tapered portion being attached to the catheter. Theballoon is expandable from a collapsed configuration, wherein theworking length and at least a portion of each tapered portion aresubstantially flattened, to an inflated configuration.

A pattern of struts are interconnected to form a stent structure havinga drug-eluting component disposed thereon that contacts the walls of alumen to maintain the patency of the vessel. In one aspect, at least oneof the struts may have a variable thickness. The stent structure anddrug-eluting component have first and second ends with each endincluding a tapered portion. Further, the stent structure anddrug-eluting component are disposed over the balloon such that thetapered balloon first and second ends are covered by the stent structureand drug-eluting component. The drug-eluting component can be pre-loadedwith a therapeutic drug for the eventual release thereof at a treatmentsite.

It should be appreciated that the drug-eluting stent delivery system ofthe present invention may be utilized in any part of the vasculatureincluding neurological, carotid, coronary, renal, aortic, iliac,femoral, or other peripheral vasculature.

An additional aspect of this invention provides a method of making adrug-eluting stent delivery system for the treatment of edge restenosiswithin a reference vessel. One particular embodiment of making thedrug-eluting stent delivery system includes providing a tubularcatheter. A balloon is then positioned about at least a portion of thecatheter with the balloon having a first end and a second end and aworking length therebetween. Each balloon end includes a tapered portionwith each tapered portion being attached to the catheter. The balloon isinflatable from a collapsed configuration, wherein the working lengthand at least a portion of each tapered portion are substantiallyflattened, to an inflated configuration.

The method of making the drug-eluting stent delivery system of thepresent invention further includes providing a drug-eluting stent thatcontacts the walls of a lumen to maintain the patency of the vessel. Thedrug-eluting stent has a first end and a second end with each endincluding a tapered portion. The drug-eluting stent is positioned overthe balloon such that at least a portion of the tapered balloon firstand second ends are covered by the drug-eluting stent. A therapeuticdrug can be loaded into the drug-eluting stent for the eventual releasethereof at a treatment site.

Other features and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view, partially in section, of a non-taperedstent which is mounted on a delivery catheter and disposed within adamaged artery.

FIG. 2 is an elevational view, partially in section, similar to thatshown in FIG. 1 wherein the stent is expanded within a damaged artery.

FIG. 3 is an elevational view, partially in section, depicting theexpanded stent within the artery after withdrawal of the deliverycatheter.

FIG. 4 is a plan view of a flattened stent of the invention whichillustrates the pattern of the stent shown in FIGS. 1-3 in an unexpandedcondition.

FIG. 5 is a cross-sectional view of a hypothesized pattern of edgerestenosis as a result of injury in the shoulder region of the vesselcombined with the absence of drug therapy when a non-tapered stent isused for treatment.

FIG. 6 is a flattened, plan view of a non-tapered stent having a polymercoating disposed thereon.

FIG. 7 is a cross-sectional view of the drug-eluting, tapered stentdelivery system in accordance with the present invention.

FIG. 8 is an enlarged, cross-sectional view of the tapered portion ofthe drug-eluting stent delivery system of FIG. 7.

FIG. 9 is an enlarged, cross-sectional view of the drug-eluting, taperedstent delivery system in accordance with the present invention.

FIG. 10 is a cross-sectional view of an alternative embodiment of thedrug-eluting, tapered stent delivery system in accordance with thepresent invention.

FIG. 11 is a flattened, plan view of a tapered stent with a conformalpolymer coating disposed thereon illustrating a reduced number of ringsin each shoulder region of the stent.

FIG. 12 is a flattened, plan view of the tapered stent of FIG. 11 in anexpanded condition.

FIG. 13 is a flattened, plan view of an alternative embodiment of thedrug-eluting tapered stent in accordance with the present invention.

FIG. 14 is a flattened, plan view of the drug-eluting, tapered stentwith a variable thickness in accordance with the present invention.

FIG. 15 is a cross-sectional view of a drug-eluting, tapered stentdelivery system of the invention with the drug-eluting, tapered stentcorresponding to each end of the balloon shoulder region while in thereference vessel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a drug-eluting stent deliverysystem for the treatment of edge restenosis in a blood vessel. Inparticular, the present invention includes a drug-eluting stent havingtapered end portions that extend the region of drug treatment into thestent shoulder regions of the vessel. Accordingly, as a result of theoptimal design of the drug-eluting stent delivery system, balloon injuryin the shoulder region is practically non-existent as the tapereddrug-eluting stent effectively covers the balloon in this area. A stentthat is continuous in the balloon shoulder or taper region, rather thanending abruptly at the start of the shoulder or taper region, along withdrug-eluting stent therapy in the shoulder region, can significantlyreduce the incidence of edge or in-segment restenosis.

Referring to the drawings, FIG. 1 depicts a metallic (untapered) stent10 mounted on a catheter assembly 12 which is used to deliver the stentand implant it in a body lumen, such as a coronary artery, carotidartery, peripheral artery, or other vessel or lumen within the body. Thestent generally comprises a plurality of radially expandable cylindricalrings 11 disposed generally coaxially and interconnected by undulatinglinks 15 disposed between adjacent cylindrical elements. The catheterassembly includes a catheter shaft 13 which has a proximal end 14 and adistal end 16. The catheter assembly is configured to advance throughthe patient's vascular system by advancing over a guide wire by any ofthe well known methods of an over the wire catheter system (not shown)or a rapid exchange catheter system, such as the one shown in FIG. 1.

Catheter assembly 12 as depicted in FIG. 1 is of the well known rapidexchange type which includes an RX port 20 where the guide wire 18 willexit the catheter. The distal end of the guide wire 18 exits thecatheter distal end 16 so that the catheter advances along the guidewire on a section of the catheter between the RX port 20 and thecatheter distal end 16. As is known in the art, the guide wire lumenwhich receives the guide wire is sized for receiving various diameterguide wires to suit a particular application. The stent is mounted onthe expandable member 22 (balloon) and is crimped tightly thereon sothat the stent and expandable member present a low profile diameter fordelivery through the arteries.

As shown in FIG. 1, a partial cross-section of an artery 24 is shownwith a small amount of plaque that has been previously treated by anangioplasty or other repair procedure. Stent 10 of the present inventionis used to repair a diseased or damaged arterial wall which may includethe plaque 25 as shown in FIG. 1, or a dissection, or a flap which arecommonly found in the coronary arteries, carotid arteries, peripheralarteries and other vessels.

In a typical procedure to implant stent 10, the guide wire 18 isadvanced through the patient's vascular system by well known methods sothat the distal end of the guide wire is advanced past the plaque ordiseased area 25. Prior to implanting the stent, the cardiologist maywish to perform an angioplasty procedure or other procedure (i.e.,atherectomy) in order to open the vessel and remodel the diseased area.Thereafter, the stent delivery catheter assembly 12 is advanced over theguide wire so that the stent is positioned in the target area. Theexpandable member or balloon 22 is inflated by well known means so thatit expands radially outwardly and in turn expands the stent radiallyoutwardly until the stent is apposed to the vessel wall. The expandablemember is then deflated and the catheter withdrawn from the patient'svascular system. The guide wire typically is left in the lumen forpost-dilatation procedures, if any, and subsequently is withdrawn fromthe patient's vascular system. As depicted in FIGS. 2 and 3, the balloonis fully inflated with the stent expanded and pressed against the vesselwall, and in FIG. 3, the implanted stent remains in the vessel after theballoon has been deflated and the catheter assembly and guide wire havebeen withdrawn from the patient.

The stent 10 serves to hold open the artery 24 after the catheter iswithdrawn, as illustrated by FIG. 3. Due to the formation of the stentfrom an elongated tubular member, the undulating components 15 of thestent are relatively flat in transverse cross-section, so that when thestent is expanded, it is pressed into the wall of the artery and as aresult does not interfere with the blood flow through the artery. Thestent is pressed into the wall of the artery and will eventually becovered with endothelial cell growth which further minimizes blood flowinterference. The undulating portion of the stent provides good tackingcharacteristics to prevent stent movement within the artery.Furthermore, the closely spaced cylindrical elements at regularintervals provide uniform support for the wall of the artery, andconsequently are well adapted to tack up and hold in place small flapsor dissections in the wall of the artery.

The stent patterns shown in FIGS. 1-3 are for illustration purposes onlyand can vary in size and shape to accommodate different vessels or bodylumens. Further, the metallic stent 10 is of a type that can be used inaccordance with the present invention. FIG. 4 is a plan view of aflattened stent which illustrates the pattern of the stent shown inFIGS. 1-3 in an unexpanded condition. The stent can be made to havetapered ends in accordance with the present invention as furtherdisclosed herein. The stent 10 is shown in a flattened condition so thatthe pattern can be clearly viewed, even though the stent is never inthis form. The stent is typically formed from a tubular member, however,it can be formed from a flat sheet such as shown in FIG. 4 and rolledinto a cylindrical configuration.

It should be appreciated that the drug-eluting stent delivery system ofthe present invention is applicable to all vascular stent applicationsin the body including neurological, carotid, coronary, renal, aortic,iliac, femoral, and other peripheral vasculature.

FIG. 5 illustrates a cross-sectional view of a hypothesized pattern ofedge restenosis 26 as a result of injury in the shoulder region of thevessel combined with the absence of drug therapy when a stent 10 (i.e.,untapered) is used for treatment. As shown in FIG. 5, the characteristic“candy-wrapper” ends 27 are particularly apparent in the regionsurrounding the proximal and distal ends of the implanted stent. Inaddition, the area of the blood vessel where the expanded stent ispositioned shows signs of sustained damage 30 from vessel stretch andmechanical damage from the in-stent section itself. Although the stentis not present at the stent shoulder, there is still injury as a resultof vessel stretch. Further, there is a significant potential formechanical injury at the stent edge 32 due to the arterial wall stressaccumulation at the stent edge. The tapered, drug-eluting stent deliverysystem of the present invention resolves the aforementioned issues as aresult of the optimal design of the tapered, drug-eluting stent, whichis described in further detail herein.

FIG. 5 illustrates a cross-sectional view of a hypothesized pattern ofedge restenosis 26 as a result of injury in the shoulder region of thevessel combined with the absence of drug therapy when a stent 10 (i.e.,untapered) is used for treatment. As shown in FIG. 5, the characteristic“candy-wrapper” ends 27 are particularly apparent in the regionsurrounding the proximal and distal ends of the implanted stent. Inaddition, the area of the blood vessel where the expanded stent ispositioned shows signs of sustained damage 30 from vessel stretch andmechanical damage from the in-stent section itself. Although the stentis not present at the stent shoulder, there is still injury as a resultof vessel stretch. Further, there is a significant potential formechanical injury at the stent edge 32 due to the arterial wall stressaccumulation at the stent edge. The tapered, drug-eluting stent deliverysystem of the present invention resolves the aforementioned issues as aresult of the optimal design of the tapered, drug-eluting stent, whichis described in further detail herein.

As will be appreciated by those having ordinary skill in the art, thedrug-eluting stent 34 used in accordance with the present invention canbe virtually of any type. Any particular drug-eluting stent describedherein is for example purposes and not meant to be limiting of theinvention. FIG. 6 is an example of one such type of drug-eluting stentthat may be used in conjunction with the drug-eluting stent deliverysystem of the invention. In particular, FIG. 6 depicts an elevationalview of a stent 10 having a conformal polymer coating 38 disposedthereon. The polymer is adhered to the stent using conventionalmetal-polymer adhesion techniques, such as by dipping, spraying, wiping,and brushing, which are known in the art. The aforementioned processesmay be followed by web clearing operations that can include blowing airor spinning. The conformal polymer coating can have a thickness in therange of about 1 micron to about 10 microns.

In one embodiment, the drug-eluting stent delivery system 48 of thepresent invention includes a tubular catheter 12 having a longitudinalaxis 17, as shown in FIG. 7. A balloon 40 is disposed about at least aportion of the catheter with the balloon having a first end 42 and asecond end 44 and a working length 46 therebetween. Each respectivefirst and second end of the balloon has a tapered portion 42′, 44′ and aballoon shaft 23 formed integrally with the tubular catheter. Theballoon is inflatable from a collapsed configuration, wherein theworking length and at least a portion of each tapered portion aresubstantially flattened, to an inflated configuration. A drug-elutingstent 34 contacts the walls of a blood vessel to maintain the patency ofthe vessel. The drug-eluting stent has a first end 50 and a second end52 with each end including a tapered portion 50′, 52″ respectively, ofuniform thickness. The drug-eluting stent is disposed over the balloonsuch that at least a portion of the first and second ends of the balloontapered portions are covered by the drug-eluting stent. The drug-elutingstent can be pre-loaded with a therapeutic drug, prior to beingpositioned over the balloon, for the eventual release thereof at atreatment site.

FIG. 8 depicts an enlarged, cross-sectional view of the tapered portionof the drug-eluting stent delivery system 48 of FIG. 7 with the balloonin a collapsed configuration. This collapsed configuration gives theballoon 22 (FIG. 7) of the drug-eluting stent delivery system an optimalprofile for insertion into the blood vessel. The collapsed balloon haslateral edges 54 (FIG. 7) which define a taper angle “α” extending fromthe balloon shaft 23. The edges are defined on the first and second endsof the balloon. In one embodiment, the edges define an angle measuringbetween 2 and 30 degrees relative to the longitudinal axis 17 of thecatheter. The taper angle α has the effect of minimizing frictionbetween the balloon and the blood vessel. The term “collapsedconfiguration” indicates that the balloon is not completely expanded. Inone embodiment, as shown in FIGS. 7 and 8, each respective taperedportion 42, 44′ of the balloon first end 42 and second ends 42, 44 has alength 56. Each of the tapered portions extend a distance, indicated as“l”, in a range of from about 1 mm up to about 7 mm. The distance “l” ismeasured parallel to the catheter longitudinal axis. The respectivelength for each tapered portion of the balloon first and second ends isthe same at each end. The tapered portion 42, 44′ of the balloon isformed integral with the working length 46 and the tubular catheter 12.Accordingly, the taper angle α is formed by the intersection of theballoon tapered portion and the tubular catheter. The angle β is theangle at which the balloon tapered portion meets the working length ofthe balloon.

With further reference to FIG. 7, each tapered portion 50, 52′ of thedrug-eluting stent first and second ends 50′ 52′ has a length in a rangeof from about 1 mm up to about 7 mm. The respective length for eachtapered portion of the drug-eluting stent first and second ends is thesame at each end. The tapered portion of the drug-eluting stent definesan edge 53 which, in turn, defines an acute angle α′ relative to thelongitudinal axis of the catheter. In one embodiment, the edge definesan angle measuring between 2 and 30 degrees relative to the longitudinalaxis of the catheter. The angle α′ is the angle at which the stenttapered portion extends from the balloon shaft 23. The angle β′ is theangle at which the stent tapered portion meets the working length 46 ofthe balloon. It can be appreciated that in one embodiment of theinvention, the angles α, α′, β, β′ are equivalent angles and the workinglength of the balloon is parallel to the tubular catheter.

In accordance with the invention as shown in FIG. 9, the balloon shaft23, the balloon tapered portions 42, 44, and the working length 46 eachhave respective thicknesses of 58 and 60. The thickness 64 of thetubular catheter distal end 16 is greater than the thickness of theworking length. The tapered portion of the balloon tapers from theballoon shaft to the working length. Similarly, a central portion 66 ofthe drug-eluting stent and the stent tapered portions 50, 52′ each havea respective thickness 68 and 70. The thickness of the tubular catheterdistal end 16 is also greater than the thickness of the central portion66. In one embodiment, each tapered portion of the drug-eluting stentfirst and second ends 50, 52′ may have a strut thickness in a range offrom about 25 microns up to about 200 microns.

In an alternative embodiment shown in FIG. 10, the drug-eluting stent 34tapered portions 78′ and 80′ of first and second ends 78, 80 can have adecrease in strut thickness with a knife edge. Each tapered portion ofthe drug-eluting stent may have a strut thickness in a range of fromabout 25 microns up to about 200 microns.

As illustrated in FIG. 11, the tapered drug-eluting stent 34 furtherincludes a pattern of struts having a plurality of flexible cylindricalrings 11 being expandable in a radial direction, each of the ringshaving a first delivery diameter and a second implanted diameter andbeing aligned on a common longitudinal axis 17. At least one link 15 ofthe tapered drug-eluting stent is attached between adjacent rings toform the drug-eluting stent structure. In order to maintain a consistentmetal/artery ratio in the stent first and second end tapers 50, 52′ asin the remainder of the stent, the stent pattern can be changed in thestent first and second end tapers to decrease the amount of metal insuch areas, as shown in FIG. 11. The pattern of struts can be configuredsuch that the number of cylindrical rings in each tapered portion of thedrug-eluting stent first and second ends is less than that in theremainder of the drug-eluting stent. FIG. 12 is an elevational view ofthe tapered drug-eluting stent 34 of FIG. 11 in an expanded condition.It should be appreciated that a variety of different configurations arepossible to achieve a consistent metal/artery ratio in the taper as inthe remainder of the stent, and that the example shown in FIG. 11 is notintended to be limited to such. For example, as shown in FIG. 13, thetwo outermost end rings at each end 50, 52′ can have longer struts 19.

Special consideration may also be given in sizing the tapereddrug-eluting stent 34 used in conjunction with the drug-eluting stentdelivery system 48 of the present invention. With further reference toFIGS. 11-13, the tapered drug-eluting stent includes the central portion66 that can be expanded to a size that is greater than that of thereference vessel and the balloon tapered portions 42, 44′. For example,if the reference vessel size is 3 mm, it may be desirable to have thecentral portion of the stent expanded to 3.6 mm. However, at the edge ofthe stent on the balloon taper, it may be desirable to have the stentdiameter at 3 mm. Accordingly, the stent in the shoulder regions isintentionally expanded to a different size.

In one embodiment of the invention as shown in FIG. 14, the stent may beformed so that the struts have variable thickness along the stentlength. As one example, it is contemplated that struts 74 at the ends ofthe stent may be narrower than the struts 76 in the center of the stentfor purposes of reduced vessel injury at the stent ends. When theballoon first inflates, the balloon ends have a tendency to inflate at afaster rate than the balloon center, however, with narrower struts atthe stent ends the balloon, and hence the stent, will expand moreuniformly.

FIG. 15 is a cross-sectional view of a drug-eluting, tapered stentcorresponding to each end of the balloon shoulder region whilepositioned within the reference vessel. In one embodiment, the taperedfirst and second ends of the balloon are partially covered by thedrug-eluting stent 34. The degree of coverage is selected so that thestent tapers will completely cover the tapered portion of the vesselwall that is formed when the stent is expanded to a size greater thanthat of the reference vessel. Therefore, effective drug-eluting stenttherapy is provided in the stent shoulder region when the drug-elutingstent is positioned within the vessel.

Examples of various metals or alloys used in forming the stent structureof the present invention drug-eluting stent delivery system includestainless steel, platinum, titanium, tantalum, nickel-titanium,cobalt-chromium, and alloys thereof. Examples of various polymers usedin forming the drug-eluting component of the drug-eluting stent deliverysystem for each of the embodiments include poly(methyl methacrylate)(PMMA), poly(ethylene-co-vinyl alcohol) (EVAL), poly(butyl methacrylate)(PBMA), biodegradable polymers (e.g., polyglycolic acid (PGA) andpoly(L-lactic acid) (PLLA)), copolymers and blends thereof. Thedrug-eluting component may be alternatively fabricated from variousmetals or alloys, including stainless steel, platinum, titanium,tantalum, nickel-titanium, cobalt-chromium, and alloys thereof.

Examples of therapeutic drugs or pharmacologic compounds that may beloaded into the prefabricated patterned, polymeric sleeve and deliveredto the target site in the vasculature include taxol, aspirin,prostaglandins, and the like. Various therapeutic agents such asantithrombogenic or antiproliferative drugs are used to further controllocal thrombosis. Examples of therapeutic agents or drugs that aresuitable for use in accordance with the present invention includesirolimus, everolimus, actinomycin D (ActD), taxol, paclitaxel, orderivatives and analogs thereof. Examples of agents include otherantiproliferative substances as well as antineoplastic,antiinflammatory, antiplatelet, anticoagulant, antifibrin, antithrombin,antimitotic, antibiotic, and antioxidant substances. Examples ofantineoplastics include taxol (paclitaxel and docetaxel). Furtherexamples of therapeutic drugs or agents include antiplatelets,anticoagulants, antifibrins, antiinflammatories, antithrombins, andantiproliferatives. Examples of antiplatelets, anticoagulants,antifibrins, and antithrombins include, but are not limited to, sodiumheparin, low molecular weight heparin, hirudin, argatroban, forskolin,vapiprost, prostacyclin and prostacyclin analogs, dextran,D-phe-pro-arg-chloromethylketone (synthetic antithrombin), dipyridamole,glycoprotein IIb/IIIa platelet membrane receptor antagonist, recombinanthirudin, thrombin inhibitor (available from Biogen located in Cambridge,Mass.), and 7E-3B® (an antiplatelet drug from Centocor located inMalvern, Pa.). Examples of antimitotic agents include methotrexate,azathioprine, vincristine, vinblastine, fluorouracil, adriamycin, andmutamycin. Examples of cytostatic or antiproliferative agents includeangiopeptin (a somatostatin analog from Ibsen located in the UnitedKingdom), angiotensin converting enzyme inhibitors such as CAPTOPRIL®(available from Squibb located in New York, N.Y.), CILAZAPRIL®(available from Hoffman-LaRoche located in Basel, Switzerland), orLISINOPRIL® (available from Merck located in Whitehouse Station, N.J.);calcium channel blockers (such as nifedipine), colchicine, fibroblastgrowth factor (FGF) antagonists, fish oil (omega 3-fatty acid),histamine antagonists, LOVASTATIN® (an inhibitor of HMG-CoA reductase, acholesterol lowering drug from Merck), methotrexate, monoclonalantibodies (such as platelet-derived growth factor (PDGF) receptors),nitroprusside, phosphodiesterase inhibitors, prostaglandin inhibitor(available from GlaxoSmithKline located in United Kingdom), seramin (aPDGF antagonist), serotonin blockers, steroids, thioprotease inhibitors,triazolopyrimidine (a PDGF antagonist), and nitric oxide. Othertherapeutic drugs or agents which may be appropriate includealpha-interferon, genetically engineered epithelial cells, anddexamethasone.

While the foregoing therapeutic agents have been used to prevent ortreat restenosis, they are provided by way of example and are not meantto be limiting, since other therapeutic drugs may be developed which areequally applicable for use with the present invention. The treatment ofdiseases using the above therapeutic agents are known in the art. Thecalculation of dosages, dosage rates and appropriate duration oftreatment are previously known in the art. Furthermore, the therapeuticdrugs or agents are loaded at desired concentration levels per methodswell known in the art to render the device ready for implantation.

In use, the stent is deployed using conventional techniques. Once inposition, the therapeutic drug gradually diffuses into adjacent tissueat a rate dictated by the parameters associated with the polymer coatlayer. The total dosage that is delivered is of course limited by thetotal amount of the therapeutic drug that had been loaded within thepolymeric conformal coating or other component of the drug-elutingstent. The therapeutic drug is selected to treat the deployment siteand/or locations downstream thereof. For example, deployment in thecarotid artery will serve to deliver such therapeutic drug to the localarterial tissue, and for very potent drugs, to the brain.

An additional aspect of this invention provides for a method of making adrug-eluting stent delivery system for the treatment of edge restenosisin a blood vessel. In one embodiment, the method includes providing acatheter having a longitudinal axis. A balloon 40 is positioned about atleast a portion of the catheter 16, the balloon having first and secondends 42, 44 and a working length 46 therebetween (FIG. 7). Each balloonend includes a tapered portion 42, 44, corresponding to respective firstand second ends, with each tapered portion being attached to thecatheter. The balloon is inflatable from a collapsed configuration,wherein the working length and at least a portion of each taperedportion are substantially flattened, to an inflated configuration.

The method of making the drug-eluting stent delivery system of thepresent invention further includes providing a drug-eluting stent 34(FIGS. 7 and 8) that contacts the walls of a lumen to maintain thepatency of the vessel, the drug-eluting stent having first and secondends 50, 52 and each end including a tapered portion 50, 52,respectively. The drug-eluting stent is loaded with a therapeutic drugfor the eventual release thereof at a treatment site, such as along thestent shoulder region that corresponds to the balloon tapered portionsfor the treatment of edge restenosis in the reference vessel. As shownin FIGS. 7 and 8, the means for positioning the drug-eluting stent overthe balloon is accomplished in such a manner such that at least aportion of the tapered balloon first and second ends 42, 44′ are coveredby the drug-eluting stent.

The drug-loaded stent can be processed directly by methods known in theart, such as by spray or dip coating. In this case, for example, thedrug/polymer coated stent is first prepared by coating the bare metalstent. Next, the stent is crimped and securely attached to the balloonusing current technology to produce the final drug eluting stentdelivery system. If a polymeric, drug impregnated, sleeve is used, thesleeve is fabricated separately and then attached to the outer surfaceof the stent using various metal-polymer and polymer-polymer bondingtechnologies such as adhesives, solvent welding, or hot melt attachment.This may be done before, or after, the stent is crimped onto the ballooncatheter.

The aforedescribed illustrative stent 34, 36 of the present inventionand similar stent structures can be made in many ways. One method ofmaking the stent rings 11 is to cut a tubular member, such as stainlesssteel tubing to remove portions of the tubing in the desired pattern forthe stent, leaving relatively untouched the portions of the metallictubing which are to form the rings. In accordance with the invention, itis preferred to cut the tubing in the desired pattern using amachine-controlled laser process which is well known in the art.

The foregoing laser cutting process to form the cylindrical rings 11 canbe used with metals other than stainless steel includingcobalt-chromium, titanium, tantalum, platinum, nickel-titanium, andalloys thereof, and other biocompatible metals suitable for use inhumans, and typically used for intravascular stents. Further, while theformation of the cylindrical rings is described in detail, otherprocesses of forming the rings are possible and are known in the art,such as by using chemical etching, electronic discharge machining,stamping, and other processes.

While the invention has been illustrated and described, it will beapparent to those skilled in the art that various modifications andimprovements can be made without departing from the spirit and scope ofthe invention. Further, particular sizes and dimensions, materials used,and the like have been described herein and are provided as examplesonly. Likewise, the invention is not limited to any particular method offorming the underlying medical device structure. Accordingly, it is notintended that the invention be limited, except as by the appendedclaims.

1. A method of making a drug-eluting stent delivery system for thetreatment of edge restenosis in a blood vessel, comprising: providing atubular catheter; positioning a balloon about at least a portion of thecatheter, the balloon having a first end and a second end and a workinglength therebetween, the first end and the second end each including atapered portion, each tapered portion being attached to the catheter,the balloon being inflatable from a collapsed configuration, wherein theworking length and at least a portion of each tapered portion aresubstantially flattened, to an inflated configuration; providing adrug-eluting stent configured to contact a wall of a blood vessel so asto maintain the patency of the vessel, the drug-eluting stent having afirst end and a second end, the first end and the second end eachincluding a tapered portion; loading the drug-eluting stent with atherapeutic drug; and positioning the drug-eluting stent over theballoon such that at least a portion of the first end and the second endof the balloon are covered by the tapered portion of the drug-elutingstent; wherein the balloon in a collapsed configuration includes a taperangle of 2 degrees to 30 degrees as measured from lateral edges of theballoon relative to a longitudinal axis of the catheter.
 2. The methodof claim 1, wherein the balloon shaft is formed integrally with thetubular catheter.
 3. The method of claim 1, wherein the drug elutingstent contacts the walls of the blood vessel to maintain the patency ofthe blood vessel.
 4. The method of claim 1, wherein the first end andthe second end of the stent have a tapered portion having a uniformthickness.
 5. The method of claim 1, wherein the therapeutic drug ispreloaded on the stent prior to mounting the stent on the balloon. 6.The method of claim 1, wherein the tapered portion of the first end andthe second end of the balloon minimize friction between the balloon andthe blood vessel during delivery of the drug eluting stent in a bloodvessel.
 7. The method of claim 1, wherein the tapered portion of thefirst end and the second end of the balloon extends a length in a rangefrom about 1 mm to about 7 mm.
 8. The method of claim 7, wherein thelength of the tapered portions of the first end and the second end ofthe balloon are substantially equal.